Shifting sands in time

November 20, 2023

By Dr. Jeffrey Schmid
Environmental Research Manager

In the ever-shifting landscapes of Southwest Florida’s beaches, loggerhead turtles have emerged as symbols of resilience and adaptability. Despite the formidable challenges posed by Hurricane Ian, the 2023 nesting season on Keewaydin Island was a successful one. Conservancy staff and interns recorded an impressive 526 nests, surpassing expectations in a year with dramatic environmental events. This success, however, was not without its hurdles. The storm’s aftermath left a trail of debris and altered beach profiles, leading to a record 928 non-nesting emergences, or false crawls. Yet, the determination of these ancient mariners prevailed, with over 34,000 hatchlings believed to have reached the Gulf, showcasing the resilience of these turtles in a changing environment.

Hurricane Idalia formed at the end of August and, although the center of circulation remained well offshore, coastal areas in southwest Florida experienced flooding from the storm surge generated by strong onshore winds. Making matters worse, exceptionally high tides (“King tides”) from a rare blue supermoon combined with the wind-driven surge to create much higher storm tides. As with Ian’s landfall to the north, narrow and low-elevation barrier islands such as Keewaydin were washed over by Idlaia’s storm tides. Fortunately, the turtle hatching season was almost over and most of the tiny hatchlings had already emerged from the nests.

Our post-Idalia survey revealed drastic changes to the beaches on Keewaydin, similar to those observed after Ian the previous year. Rough surf had caused substantial erosion to the lower portion of the beach while the high tides and storm surge pushed the sand further inland. The turtle nests that remained before the storm were either washed away or covered with a foot or two of compacted sand. ATV trails along the north end of the island had to be re-routed around all the stumps and snags that had been uncovered during the storm tides. Interestingly, a couple of coastal survey markers, or range monuments, that had apparently been buried in the sand beforehand were now found exposed near the water’s edge.

Range monuments were deployed along Florida’s coast in the 1970s to monitor changes to beach profiles. Coastal engineers and surveyors also use these markers as a reference for beach restoration/renourishment projects. We use a similar system of numbered PVC poles at 500-foot intervals on Keewaydin for referencing the location of turtle nests. The range monuments consisted of 4” x 4” x 4’ concrete posts placed at 1,000-foot intervals, and each post has a brass disc on top with information designating each individual range monument. The monuments observed after Idalia’s storm tides were “R-97, deployed in 1973, and “T-98”, deployed in 1978.

What’s most intriguing about the newly discovered range monuments is their location after Idalia relative to where they were initially deployed some 45 years ago. Archived photographs indicate the monuments were placed in the vegetation behind the “dune” area, such as it is on our relatively low wave energy beaches. The shoreline vegetation on Keewaydin in the 1970s consisted of dense stands of Australian pine (Source: COASTS), an invasive tree species that was later removed from most of the island in the late 1990s to restore native vegetation.

After Idalia, the monuments were now located further down the beach in the tidal zone and are also accompanied by large stumps that appear to be leftovers from the Australian pine removal. These features have not moved but rather the beach and dune system have migrated inland. The “dome home” formerly on Cape Romano is another classic example of the dynamic nature of our coastlines.

Despite these shifting sands, the female loggerheads have returned to nest on barrier islands such as Keewaydin year after year. A testament to the persistence of these ancient mariners. The Conservancy has been collecting data from loggerheads nesting on Keewaydin for the past four decades. Additionally, Rookery Bay National Estuarine Research Reserve has been monitoring shoreline change on the island since 1998 following the removal of Australian pines.

The location of turtle nests on Keewaydin could be analyzed relative to the changes in the beach profile over the past 35 years and possibly demonstrate the resiliency of this species in the face of a dynamic environment. Perhaps there are lessons to be learned from sea turtles, who have been crawling ashore beaches since the dinosaur era and have survived through extended and sometimes drastic climatic changes.